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Photoshop Masking and Compositing: Fundamentals is the introductory installment of Deke McClelland's four-part series on making photorealistic compositions in Photoshop. The course shows how to make selections, refine the selections with masks, and then combine them in new ways, using layer effects, blend modes, and other techniques to create a single seamless piece of artwork. Deke introduces the Channels panel and the alpha channel, the key to masking and transparency in Photoshop; reviews the selection tools, including the Color Range tool , Quick Mask mode, and the Refine Edge command; and shows how to blend masked images so they interact naturally.
In this exercise we're going to take a look at these three check boxes that are available in the options bar when you're using the Magic Wand tool. We'll start with Contiguous, very easy to understand, then Sample All Layers, and finally the biggest concept of them all, which is Anti-aliasing. I've gone ahead and re-established the default settings for the Magic Wand tool, and I've restored the saved version of the Gradient demo file. I'm working on a Background layer, as you can see. If I go ahead and click in this top gradient, I select only the adjacent pixels by default. In other words, I don't jump across that blue gap.
However, if I turn off Contiguous, which is essentially just another word for adjacent, and then I go ahead and click at that same spot again, notice this time I jumped the gap. So the fact that this blue bar is in the way no longer matters. All right, I'll go ahead and press Ctrl+D or Command +D on the Mac to deselect that area and I'm going to turn Contiguous back on, and I'll go ahead and click inside that region once again to select that small portion of the top gradient. I want you to know that there's a couple of commands that work in combination with the Magic Wand tool that take advantage of both Tolerance and Contiguous and they are these; under the Select menu there is Grow and Similar.
So the Grow value goes ahead and expands the existing selection by the Tolerance value that you've dialed in with the Magic Wand tool. So notice, I went ahead and grew the selection in either direction, once again, using a Tolerance of 34, however, I only selected adjacent pixels. If you want to grow the selection and select nonadjacent pixels, then you choose this command, Similar, which I've given a keyboard shortcut. So if you loaded DekeKeys, you can press Ctrl+Shift+Alt+M or Command+Shift+Option+M on the Mac.
And notice, this command will go ahead and once again expand the selection outline. So this is what it looked like before, this is what it looks like now. So it expands the selection by that Tolerance value and it goes ahead and jumps the gap. So in other words, if you dial in a higher Tolerance value, let's say I go ahead and take that guy up to 100, and then I go to the Select menu and choose either Grow or Similar in this case, really doesn't matter, because we've already jumped the gap at this point, notice how much more dramatically that selection outline grows.
And so if for no other reason than using these two commands, you want to understand the functionality of the Magic Wand tool, because you can use these commands with the selection that you created using any tool inside of Photoshop. All right. Bearing that in mind, let's move on here. The next item is Sample All layers. Currently we're only paying attention to the content of the layer that we're working on, which is the Background layer. So if I turn on these other layers, thing 1, thing 2, and thing 3, for example, and I go ahead and press Ctrl+ D or Command+D on the Mac so that I can start my selection outline over, and I click inside this top gradient, all those other layers are ignored.
However, if I turn on Sample All layers, then Photoshop will now pay attention to the contents of those layers. So if I press Ctrl+D or Command+D on the Mac and I click, let's say, right about there, then I only select that composite region. So that check box is all about setting the Magic Wand tool, so it pays attention to the entire composition. However, always bear in mind you're only working on one layer at a time. All right. I'm going to go ahead and turn that check box back off, press Ctrl+D or Command+D on the Mac to deselect the image and turn off these other layers.
Now let's talk about Anti-alias. Now, Anti-aliasing is all about trying to represent curves using square pixels. To understand why it's called Anti-aliasing, I've got this file called checkers.psd. And notice if there was no blurring of pixels, so that, for example, we're representing these checkers descending into the horizon, and each pixel is either black or white and that's it, there's no averaging whatsoever, then we end up with this aliasing effect in the background.
In other words, the checkers are breaking down and they don't look right anymore. The solution is Anti-aliasing, and let me show you what that looks like. This time I've got a file opened called Antialiasing demo.psd. Notice I have this layer here called pixel grid. So imagine that we're looking at these big pixels, all of which are currently white. Now, I am going to switch to the Paths panel for a moment and click on this circle in order to select it. And you can see we've got something of a problem here. We are representing a circle using square pixels is concerned, because the real mathematical definition of the circle cuts through many of these pixels.
So if I switch back to Layers panel and turn on this layer called Jagged, that's what the circle would look like if there was no Anti-aliasing. If the pixels were either just turned on or off, and that's it. I'll go ahead and turn that layer off, and then I'll turn on Anti-alias. And you can see what Photoshop is doing when it's creating these soft edges is that it's computing the Opacity of each and every pixel based on how much that mathematical definition of the circle cuts through it.
So if the pixel is mostly inside the circle, it's mostly opaque. If it's mostly outside the circle, it's mostly transparent. And that's where that little bit of softening that's called Anti-aliasing comes from. All right. Let's switch back to the Gradient demo file once again. Now, I should mention that Anti- aliasing is associated with a bunch of tools. You don't need it for the Rectangular Marquee tool, but you do for the Elliptical Marquee tool, because after all it's drawing ellipses and you have to reconcile those curves inside of those square pixels.
You also have Anti-aliasing when working with the Lasso tools, and it's handled very well in the case of both the Lasso and the Ellipse. It's not handled nearly so well where the Magic Wand tool is concerned. In fact, I'll go ahead and click in order to create a selection here. Tolerance value happens to be 100, that doesn't really matter. I'm going to switch to the Channels panel and I am going to drop down to that icon there, Save selection as channel, I'll go ahead and click on it to create an Alpha Channel version of the selection.
Then, I'll click on Alpha 1, so we can see it, and I'll press Ctrl+D or Command+D on the Mac to deselect the image, and let's go ahead and Zoom in. And what we have is an awful lot of jags. And that's because where the Magic Wand is concerned, there is no mathematical definition of anything. There is no curve that Photoshop is trying to reconcile. So the Anti-aliasing that gets applied is a kind of sham frankly and sometimes it just doesn't work at all, as in the case of this gradient. And that's why, that alone right there, is why the Magic Wand tool has such a bad reputation, because it ends up oftentimes creating jagged edges like this.
However, under the right circumstances you can get much better results, and I'm going to show you what those circumstances look like when we put the tool to work, starting in the very next exercise.
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